Using highly purified src kinase from RSV induced rat tumors, S. Ito and co-workers have shown that vinculin, an in vivo substrate for the kinase, is also phosphorylated by the kinase in cell-free extracts. This phosphorylation is stimulated by anionic phospholipids. To determine the mechanism for this stimulation, S. Ito has measured the interaction of anionic phospholipids with vinculin and shown that vinculin binds to acidic phospholipids but not neutral phospholipids. Therefore one mechanism by which phospholipids promote vinculin phosphorylation is by binding to the substrate. C. Roth has found that RSV transformed Chinese hamster ovary (CHO) cells are resistant to the growth inhibitory action of cyclic AMP. In these resistant cells cyclic AMP stimulates the phosphorylation of pp60src and increases src kinase activity. These findings raise the intriguing possibility that RSV transformation changes the response of the cell to cylic AMP so that instead of being an inhibitory factor it is converted to a stimulatory factor.